<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="out">
        <div class="inner"></div>
    </div>
</body>
<style>
    .out {
        background-color: black;
        padding: 10px;
    }

    .inner {
        background-color: #f90;
        width: 100px;
        height: 100px;
        float: left;
    }

    .out::after,
    .out::before {
        content: "";
        display: table;
        clear: both;
    }
</style>

</html>